The present invention relates to the art of image processing. It finds particular application in conjunction with cleaning up images generated by computerized tomographic scanners and will be described with particular reference thereto. However, it is to be appreciated that the invention may also find application in conjunction with other diagnostic images, particularly images generated using a convolution and backprojection or analogous processing technique.
Each CT scanner image conventionally represents a plane about one or one and a half millimeters to ten millimeters thick through the subject. For greater diagnostic value, a series of images are commonly generated, each representing an adjacent or closely adjacent plane.
To provide images with good resolution, there are a large multiplicity of samplings per image. In fourth generation scanners, the scan circle may be surrounded by one thousand, two thousand, four thousand, or more detectors, about a quarter of which are irradiated at any given time. The irradiated detectors are repeatedly sampled as the x-ray source rotates about the examination region. Thus, a very large number of data samplings are generated per image. Several images, e.g. ten or twenty, may be generated per study. In order to freeze the region of interest of the subject and eliminate motion defects, the multiple images are generated as quickly as possible.
The multiple samplings are assembled into data lines which are convolved and backprojected into an image representation. Various processing techniques have been developed in order to generate the resultant images quickly. Various hardware advantages and cost reductions are achieved when the data lines or views are processed as fast as they are generated. This enables the massive amount of raw data values which are used to construct the series of images for each diagnostic study to be discarded as each is processed. Rather than saving raw data, only the series of images, which also represents a massive data storage commitment, is retained.
From time to time, one of the thousands of detectors in the scanner array will go bad and give an aberration at each sampling. When these bad data values are convolved and backprojected with the multiplicity of good data values, streaks are caused in the resultant image. These streaks disrupt the resultant image and often render them useless for diagnostic purposes. Moreover, when a detector goes bad, or intermittently puts out bad data, all of the images within a single study are commonly affected.
The simple solution to a set of streaked diagnostic images is to put the patient back in the scanner and generate a new set. However, this is not always advisable or even possible. In some studies, a contrast agent is injected into the patient's blood as a part of the diagnostic scanning procedure. To get good contrast, it may be necessary to wait for the first dose of contract agent to be out of the patient's system. Further, it is advantageous to minimize patient dosage of the contrast agents to avoid any potential physiological reactions to the agents. In other instances, the patient has already left the hospital or facility. The scanner and scanning procedure is in many instances conducted by a technician to generate the set of diagnostic images which are reviewed at a different location or at a different time by the radiologist. Also, it may not be advisable to re-radiate the patient by conducting another scanning procedure.